Poly-gamma-esters of optically active glutamic acid



United States Patent Ofiice 3,119,794 Patented Jan. 28, 1964 This invention relates to superior new polymers. More particularly, this invention is concerned with novel high molecular weight polypeptides which exhibit remarkable thickening powers.

Constant eilort is being made to produce lubricants which exhibit relatively little change in viscosity over a wide range of temperatures. Thus, in any application where a lubricant is subject to use in wide variations of temperature, it is desirable that the lubricant have not too high a viscosity at the lower temperatures, nor too low a viscosity at the higher temperatures. For effective lubrication the oil must not become so viscous at the lower temperatures so as to impede starting and cause excessive wear, and not become so thin at the higher temperatures so as to fail to provide adequate separation of the wearing surfaces.

With regard to lubricating oils, these desired viscositytemperature characteristics may be obtained in some measure by the incorporation of certain synthetic prodnets of large molecular size and companative chemical inertness. These products are known as viscosity index (t .1.) improvers. However, any initial rise in V.I. attributable to the incorporation of the high molecular weight product will diminish upon operation-f the machinery due to the shear forces set up by the moving parts of the machinery, for example, as in an internal combustion engine. These forces serve to shear the high molecular weight additive into component parts of lower molecular weight, yielding in turn a lower V.I. It can thus readily be seen that a high resistance to shear degradation is an exceptionally desirable property of a V.I. improver. A further highly desirable property of a VI. improver is that the desired improvement in VI. can be achieved by the addition to the lubricating oil of a small percent by weight of the additive.

It hm now been found that a novel class of oil-soluble high molecular weight polypeptides derived from esters of optically-active glutamic acid exhibit remarkably each of the above described highly desirable properties. These novel polypeptides provide surprisingly effective thickening at low concentrations. Further, these novel polypeptides display a highly remarkable resistance to permanent shear degradation. This unusual combination of effective thickening power, law percent 'by weight additive requirement, and excellent shear strength, makes these novel polypeptides particularly desirable and useful as V. I. improvers.

These polypeptides may also be used as thickeningagents in paints or 'asphalts. It has further been found that these novel polypeptides are surprisingly effective as anti bleeding agents in greases.

The polypeptides of the present invention have the following general formula:

where R is selected from the group consisting of benzyl radicals and alkyl radicals containing from 8 to '18 carbon atoms. The benzyl radical will occupy from 0 to 30 mol. percent of the ester radical (R) positions and the alkyl radical will occupy from 70 to 100 mol. percent of the ester radical positions. The molecular weight of the polymer will range from 10,000 to 1,000,000 with n 2 being the number of recurring units necessarily corresponding to the molecular weight.

These polyesters may be suitably prepared by transesteriflcation of polybenzyl glutamate with the appropriate alcohol, or by direct synthesis from the glutamate monomet. The following specific examples will serve to illustr-ate the preparation of the products of the present invention, in particular, polylauryl glutamate.

EXAMPLE I Trans-esteriflcation of polybenzyl glutamate: A 14.49 g. quantity of poly-y-benzyl-bglutarrrate is dissolved in 250 cc. of dry chloroform. 170 cc. of dry lauryl alcohol is added with stirring and h ating, along with 20 cc. of a mixture made from 7.86 g. of p-toluene sulfonic acid monohydrate and 600 cc. of benzene, wherein all water was removed by azeotroping. The mixture is refluxed for 48 hours, thereafter the solution is kept at "100 C. for 6 hours. At the end of this time no polymer should precipitate upon the addition of isooctane. The polymer is now precipitated by pouring the solution into excess methanol and filtering. The product is a white, fibrous polymer having a composition corresponding to 87% polylauryl glutamate and 13% polybenzyl glutamate, and having an estimated average molecular weight of about 150,300 as determined by viscosity measurements.

EXAMFLE II Direct synthesis from the glutamate monomer: 145 g. of glutamic acid is suspended in a mixture of 1 liter of dry distilled lauryl alcohol and '1 liter of sodium dried dioxane. 2.50 ml. of concentrated HCl (36%) is added and the mixture heated at C. with stirring until the glutamic acid is dissolved. The solution is cooled to room tempenature and diluted with 2 volumes of ether. After 3 hours, the crystallization of lauryl glutamate hydrochloride is complete. 'The crystals are filtered and washed with pentane. Yield, 43.5 g. of the hydrochloride as shi l.- mering flakes. Then the anhydride is prepared by suspending 60 g. of the hydrochloride in dry chloroform and bubbling phosgene through the refluxing solution with vigorous stirring until a clear solution is obtained (approx. 6 hours). After vacuum removal of the excess phosgene and solvent the residue is diluted with a dry n-heptane and the solution cooled to 0 C. Crystallization, initiated by scratching, is complete after 12 hours. After ltration the solution is recrystallized at 30 C., collected and dried. Yield, 25 g. of the anhydride as colorless flakes. Polymerization is accomplished by dissolving 5 g. of the anhydride in 100 cc. of dry benzene and adding 0.1 cc. of a solution of 36 -mg./ cc. of triethylamine in dry benzene. After standing for 40 hours, the viscous solution is poured into methanol and the precipitated polymer collected by filtration. The polylauryl glutamate product is a white, fibrous solid somewhat sticky to the touch. Yield, completion of the reaction based upon the anhydride.

Calculated 69. 63 10. 52 4. 70 Found 68. 53 10. 38 4. 92

weight polyglntamate additive is observed. The V1. is determined by ASTM Standard Method D5674l. The shear loss is determined by applying shear forces in the form of cavitations induced by ultrasonic waves and measuring the change in viscosity at 210 F. before and after cavitation. The polyglutamate employed is the transesterification reaction product of poly-'y-benzyl-L-glutamate and lauryl alcohol, having a composition corresponding to approximately 90% polylauryl glutamate and 10% polyberizyl glutamate. Samples numbers 1 through 5 have an average molecular weight of about 500,000 and sample number 6 has an average molecular weight of about 160,000.

Table II illustrates the superior thickening power of the above described polyglutamate as compared to commercinlly acceptable V.I. improvers. Acryloid 763 is a polymethacrylate V.I. improver having an average molecular weight of about 400,000, sold by Rohm & Haas. Paratone N is a polybutylene V.I. improver having an average molecular weight of about 120,000, sold by Enjay Co. The amount of additive that must be incorporated in 150 N oil to raise the viscosity of the oil at 210 F. to 67.2 SSU is measured and compared.

Table II COBIPARATIVE THICKENING POWERS Polyglu- Acryloid Paratone tamate 763 N \Veight percent additive required to yield oil of equal viscosity 0. 5 3.05 3.

Table III illustrates the superior shear performance of the present invention as compared to the above mentioned commercial additives. The shear loss is determined by the method described above. The oil tested is at an additive concentration that will yield an oil of 67.2 viscosity, SSU at 210 F.

Table III COMPARATIVE SHEAR STRENGTH Polyglu- Acryloid Paratone tamnte 763 N Percent Shear Loss (A Viscosity 210 F.) 2. 8 30. 0 6.0

From the tests in Table I, it will be seen that each of the illustrative compositions containing the polyglutamate thickener possess remarkably improved viscosity-temperature properties compared to the base oil alone. Further, this improvement in viscosity-temperature behavior is achieved with the incorporation of a surprisingly small percent by weght of the polyglutamate, as is illustrated by Table II above. By comparison, commercially acceptable V.I. improvers such as the Acryloids or Paratones are normally employed in the amount of 1 to by Weight of the lubricating oil solution, whereas, approximately A of a percent by weightof the present invention provides sufiicient thickening. Specifically, to raise the viscosity of 150 Neutral oil to 67.2 SSU at 210 F., 6 times more Acryloid 763 or Paratone N is required than is required of the polyglntamate thickener; see Table II.

Table IV Sample 1 Sample 2 (A) Grease Composition:

Base Grease, Percent 99 Polyglutamnte, Percent 1 (B) Physical Characteristics:

ASIM dropping Point, F 466 456 AS'IM Worked penetration, P60 at 77 F 300 346 Oil Separation, PercenL 3. 0 1.6

As can be seen, an addition of only 1% by weight of the polyglutamate reduces grease bleeding by over 50% as compared to the base grease alone.

We claim:

1. Poly-gamma-esters of optically active glutamic acid consisting essentially of recurring units of the following formula:

COOR

wherein said gamma-ester R radicals are selected from the group consisting of alkyl and benzyl radicals, with a major proportion of from 70 to 100 mol percent of the total R radicals consisting of alkyl radicals containing from 8 to 18 carbon atoms and the corresponding remaining proportion of from 0 to 30 mol percent of the total =R radicals consisting of benzyl radicals, the molecular weight of the polyesters ranging from 10,000 to 1,000,- 000 and n representing the number of recurring units corresponding to said molecular weight.

2. Poly-gamma-esters of optically active glutamic acid consisting essentially of recurring units of the following formula:

NHCHC O a): J

C 0 OR 11 wherein said gamma-ester R radicals are selected from the group consisting of lauryl radicals and benzyl radicals, with a major proportion from 70 to 100 mol percent of the total R radicals consisting of lauryl radicals and the corresponding remaining proportion of from 0 to 30 mol percent of the total R radicals consisting of benzyl radicals, the molecular weight of the polyesters ranging from 10,000 to 1,000,000 and n representing the number of recurring units corresponding to said molecular weight.

3. Polygamrna-esters of optically active plutamic acid consisting essentially of recurring units of the following formula:

wherein said gamma-ester R radicals are selected from the group consisting of n-octyl radicals and benzyl radi cals, with a major proportion from 70 to 100 mol percent of the total R radicals consisting of noctyl radicals and the corresponding remaining proportion of from 0 to 30 rnol percent of the total R radicals consisting of benzyl radicals, the molecular weight of the polyesters ranging from 10,000 to 1,000,000 and n representing the number of recurring units corresponding to said molecular weight.

4. Poly-gamma-esters of optically active glutarnic acid consisting essentially of recurring units of the following formula:

wherein said gamma-ester R radicals are selected firom the group consisting of tridecyl radicals and benzyl radi- References Cited in the file of this patent UNITED STATES PATENTS Lynch Mar. 16, 1948 OTHER REFERENCES Hanby et 211.: J our. Chem. Soc, 1950, pages 3239-3249; Bramford et al.: Synthetic Polypeptides, Academic Press cals, with a major proportion from 70 to 100 mol percent 15 Inc., New York, 1956, pages 42, 4'4, 51, 52 and 316-318. 

1. POLY-GAMMA-ESTERS OF OPTICALLY ACTIVE GLUTAMIC ACID CONSISTING ESSENTIALLY OF RECURRING UNITS OF THE FOLLOWING FORMULA: 